The present invention generally relates to pressure transducers and, more particularly, to the diaphragm portions of such transducers.
Pressure transducers that use piezoresistors are well known in the art. Generally, such transducers are formed with a silicon substrate and an epitaxial layer, which is grown on the substrate. A portion of the substrate is removed, leaving a thin, flexible diaphragm portion. The piezoresistors are located in the diaphragm portion to form a pressure transducer.
In operation, at least one surface of the diaphragm is exposed to a process pressure. The diaphragm deflects according to the magnitude of the pressure, and this deflection bends the attached piezoresistors. Bending of the diaphragm creates changes in the resistance value of the piezoresistors, which is reflected as a change in the output voltage signal of a resistive bridge formed at least partially by the piezoresistors.
The substrate and epitaxial layers are commonly formed of single crystal silicon. Diaphragm portions formed of single crystal silicon produce adequate results for pressures ranging from five inches H2O to 6,000 PSI. Such material does not, however, produce a high output signal with sufficient linearity at pressures below 5 inches H2O.
The following summary of the invention is provided to facilitate an understanding of some of the innovative features unique to the present invention and is not intended to be a full description. A full appreciation of the various aspects of the invention can be gained by taking the entire specification, claims, drawings, and abstract as a whole.
In accordance with certain aspects of the present invention, a method of forming a composite diaphragm for a pressure transducer or similar device is provided. The method comprises providing a substrate layer having a first conductivity type, the substrate layer having a first surface. Positive implants are deposited in the first surface of the substrate layer, and an epitaxial layer is grown on the first surface of the substrate layer so that the positive implants form positive diffusions in the epitaxial layer. An oxide pattern is formed on the epitaxial layer, and a top layer is deposited over the epitaxial layer and oxide pattern. The substrate layer and positive diffusions of the epitaxial layer are etched to form the composite diaphragm.
In accordance with additional aspects of the present invention, a composite diaphragm is provided for use in a pressure sensor or like device. The diaphragm comprises a first layer of silicon nitride and a second layer attached to the silicon nitride layer and comprising a pressure sensor pattern of silicon material.
The novel features of the present invention will become apparent to those of skill in the art upon examination of the following detailed description of the invention or can be learned by practice of the present invention. It should be understood, however, that the detailed description of the invention and the specific examples presented, while indicating certain embodiments of the present invention, are provided for illustration purposes only because various changes and modifications within the scope of the invention will become apparent to those of skill in the art from the detailed description of the invention and claims that follow.